1. Field of the Invention
The present invention relates to optical fiber telecommunication systems and, in particular, to the optical amplification modules utilized in optical amplifiers employed in such systems.
2. Technical Background
Presently, optical amplifiers for telecommunication networks are uniquely designed to meet specific customer needs in specific customer applications, according to the amplifier's role in each customer's proprietary system. There is very little commonality of either the optical designs or the physical embodiments between different amplifiers manufactured for either different customers and or different applications.
Custom design efforts add significant time and cost to the development of each amplifier. In addition, custom designs prevent achievement of efficient manufacturing scale, because only relatively few amplifiers of the same design are sold to each customer. The custom design approach also creates an inventory risk, as unsold product for one customer/application cannot be sold to another. Finally, custom designed amplifiers hinder future upgrade capability and hardware reuse.
U.S. Pat. No. 5,778,132 discloses a three “cassette” modular approach to assembly of optical amplifiers. The first cassette (first module) contains a first coil of rare earth doped optical fiber, an optical tap, an optical isolator and a wavelength division multiplexer (WDM). The second cassette (second module) contains an isolator and a WDM. The third cassette contains a second coil of rare earth doped optical fiber, a WDM, an isolator, and an optical tap. The laser sources are provided externally. The modular design approach disclosed in this patent has several shortcomings.
While this partitioning into three cassettes allows the disclosed optical amplifier to be manufactured, the three cassettes are of limited use in that they cannot be recombined to create many of today's more complex amplifiers. The disclosed partitioning of the amplifier into three cassettes does not constitute fundamental building blocks that would have wide commercial use. Furthermore, the specific cassette content does not include other components necessary for many currently available amplifier designs. For example: (a) the inclusion of the rare earth doped optical fiber in with the first and third cassettes does not allow for the manufacture of a complete, single coil amplifier; (b) the cassettes do not allow for gain flattening filters (GFFs) or variable optical attenuators (VOAs); and (c) the number and location of the bandsplitters are constrained, yet they are not always present or always present in the same configuration in commercial optical amplifiers.
Second, the cassettes are not designed to be effectively integrated. For example, the laser sources are provided externally, with no allowance for cost-effective integration of the laser sources into the cassettes.